Method for assembling and disassembling marine riser and auxiliary lines and well pressure control system

ABSTRACT

A method for assembling a riser from a platform on the surface of a body of water includes assembling segments of riser end to end through a drill floor using a main drilling unit on the platform. At least one auxiliary line is assembled from segments connected end to end through an auxiliary hoisting unit on the platform. The auxiliary hoisting unit is displaced laterally from the main drilling unit. The assembled riser is connected to a wellhead proximate the bottom of the body of water.

CROSS REFERENCE TO RELATED APPLICATIONS

Continuation of International Application No. PCT/US2017/044902 filed on Aug. 1, 2017. Priority is claimed from U.S. Provisional Application No. 62/373,543 filed on Aug. 11, 2016. Both the foregoing applications are incorporated herein by reference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable.

BACKGROUND

This disclosure relates to the field of marine petroleum drilling and production systems. More specifically, the invention relates to methods and systems for assembling and disassembling risers that connect a drilling and/or production platform on the surface of a body of water to a subsea wellhead.

Floating or other water-surface deployed structures are known in the art for drilling wellbores in formations located below the bottom of a body of water, e.g., the ocean floor, and for producing petroleum from such wellbores. The wellbores are typically drilled using fluid pressure control equipment, called a “blowout preventer” (BOP) affixed to the top of a casing cemented into a relatively shallow portion of the wellbore. A “riser”, which is a pipe formed from segments coupled end to end, is affixed to the top of the BOP and extends therefrom to the platform on the water surface. The riser may provide a conduit for fluids to move from the wellbore upwardly to the platform. Therefore a riser as used in wellbore drilling and/or later wellbore intervention may form a conduit for drilling fluid and drill cuttings to be returned to the platform for processing and recirculation into the wellbore. The riser may also be used as a conduit for moving wellbore intervention tools into and out of the wellbore from the platform. The riser may have one or more external auxiliary lines associated with the riser to communicate fluid pressure to various components in and below the riser when needed. Such lines may include, for example, choke lines, kill lines and booster lines.

A riser is assembled to the wellbore from the platform by coupling together segments, called “joints” of riser, and moving the assembled “string” of joints of riser downward from the platform as successive riser joints are coupled to the string on the platform. The foregoing procedure continues until the riser is long enough to reach the wellbore from the platform, whereupon the lowermost end of the riser is coupled to a lower marine riser package (LMRP) and the BOP. The connections are typically made by bolting a flange on each end of the riser joint to a corresponding flange on a longitudinally adjacent riser joint. The auxiliary lines may be assembled contemporaneously with assembly of the riser joints to each other. Risers known in the art include auxiliary lines coupled to an exterior of the riser and generally assembled by passing segments of the auxiliary lines through openings on flanges that connect each riser segment to adjacent riser segments. See, for example, U.S. Pat. No. 6,419,277 issued to Reynolds.

In some cases, pressure requirements of a riser and auxiliary lines may be such that using conventional auxiliary lines coupled through openings in each riser flange is impracticable. There exists a need to a method for assembling high pressure auxiliary lines that can reduce the assembly time for the entire riser system (i.e., the riser and the auxiliary lines).

SUMMARY

A method according to one aspect of the present disclosure for assembling a riser from a platform on the surface of a body of water includes assembling segments of riser end to end through a drill floor using a main drilling unit on the platform. At least one auxiliary line is assembled from segments connected end to end through an auxiliary hoisting unit on the platform. The auxiliary hoisting unit is displaced laterally from the main drilling unit. The assembled riser is connected to a wellhead proximate the bottom of the body of water.

In some embodiments, disassembling the riser may comprise reversing the actions performed in assembling the riser.

A well pressure control system according to another aspect of the present disclosure includes a riser coupled at one end to an upper end of a lower marine riser package and blowout preventer assembly. A lower end of the lower marine riser package and blowout preventer assembly is coupled to a wellhead disposed on the top of a well. The riser extends to a platform on the surface of a body of water. At least one auxiliary line extends from proximate the bottom of the body of water to the platform. The at least one auxiliary line is separate from and is disposed at a selected lateral distance from the riser. At least one fluid line hydraulically connects a lower end of the at least one auxiliary line to a part of the lower marine riser package and blowout preventer assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example embodiment of a drilling platform with a riser extending therefrom to a wellhead on the water bottom, auxiliary lines and an accumulator vessel assembly on the water bottom.

FIG. 2 shows a detailed view of the auxiliary lines.

FIG. 3 shows a detailed view of an accumulator vessel assembly.

FIG. 4 shows a more detailed view of a blowout preventer (BOP) assembly.

FIG. 5 shows a more detailed view of a portion of the riser having buoyancy devices on an exterior surface of auxiliary lines.

DETAILED DESCRIPTION

FIG. 1 shows an example embodiment of a surface deployed platform 1, which may be a floating drilling platform such as a semisubmersible drilling platform or a drill ship with dynamic positioning thrusters 2. In other embodiments, the platform 1 may be maintained in position by fixed moorings (not shown). The platform 1 is positioned approximately above a wellhead 22 on the bottom 23 of a body of water 24. Although the present description is made in terms of a semisubmersible platform, any marine platform known in the art, including without limitation bottom supported platforms, jackup drilling units and the like may be used in accordance with the present disclosure.

A main drilling unit 10 disposed on the platform 1 includes equipment (not shown separately) for raising and lowering drilling and/or wellbore intervention tools and pipe, e.g., drill pipe, into a wellbore extending into the sub-bottom below the wellhead 22 for drilling and completing the wellbore and/or for later wellbore intervention procedures. The main drilling unit 10 hoisting equipment is capable of supporting the weight of casing, tubing, riser, drill pipe and any other type of tubular and drilling and/or wellbore intervention tools needed to construct the wellbore and/or effect intervention operations in the wellbore. A riser 14 extends from the main drilling unit 10 to an upper end (explained in more detail with reference to FIG. 4) of a lower marine riser package (LMRP) and blowout preventer (BOP) assembly(“LMRP/BOP assembly”), shown generally at 16, which is itself coupled at its lower end (16B in FIG. 4) to the wellhead 22.

FIG. 5 shows a more detailed view of a portion of the riser 14, which may consist of riser segments 14A some of which are each surrounded by a buoyancy device (“buoyancy can”) 14C. The riser 14 may be assembled on the main drilling unit 10 by coupling riser segments (“joints”) 14A together end to end, some with the buoyancy cans 14C already assembled thereto or assembled to the riser 14 as it is lowered below a main drilling deck 10A of the main drilling unit 10. In some embodiments, the riser segments 14A may be coupled end to end by bolting a flange 14B at each longitudinal end of each riser segment 14A to a corresponding flange on each longitudinally adjacent riser segment.

In an example embodiment according to the present disclosure, and once again referring to FIG. 1, one or more auxiliary lines, shown generally at 18, may be assembled separately from the riser 14. The one or more auxiliary lines 18 may be, for example, a choke line, a kill line and/or a booster line. In the present example embodiment, the auxiliary lines 18 may be made from conventional threadedly connected segments of pipe used to drill the well, that is, drill pipe. The auxiliary lines 18 may be assembled from segments of conduit assembled end to end and extended into the water 24 from an auxiliary hoisting unit 12 disposed on the floating drilling platform 1. The auxiliary hoisting unit 12 may be located at a selected lateral distance from the well center (not shown separately) of the main drilling unit 10. By having an auxiliary hoisting unit 12, the auxiliary lines 18 and the riser 14 may be assembled substantially contemporaneously. In the present example embodiment, the auxiliary lines 18 may comprise threadedly connected pipe, for example, drill pipe or tubing, and thereby save substantial time in assembling the auxiliary lines 18.

The auxiliary lines 18 may be coupled to an accumulator assembly 20 at the beginning of assembly of the auxiliary lines 18. When the auxiliary lines 18 are fully assembled, the accumulator assembly 20 may be disposed on the water bottom 23. Pressurized fluid lines 20B may extend from the accumulator assembly 20 to the LMRP/BOP assembly 16. In some embodiments, the pressurized fluid lines 22 may comprise well fluid pressure control lines, e.g., choke, kill and/or boost lines hydraulically connected to the wellhead 22 below the LMRP/BOP assembly 16. In some embodiments the pressurized fluid lines 20B may comprise hydraulic fluid lines which may be used to selectively conduct hydraulic fluid under pressure to the BOP part (see FIG. 4) of the LMRP/BOP assembly 16. Hydraulic fluid under pressure may be used to operate components of the BOP part.

During riser assembly, the LMRP/BOP assembly 16 is coupled to the lowermost riser segment, and successive segments of riser are coupled end to end to the riser 14 as it is lengthened and subsequently lowered into the water 24. When the LMRP/BOP assembly 16 is just above the wellhead 22, the LMRP/BOP assembly may be coupled to the wellhead 22, for example using a remotely operated vehicle (ROV) of types known in the art. While the present example embodiment of the riser 14 may be assembled by bolting together corresponding flanges at each longitudinal end of each riser segment, it is within the scope of the present disclosure to use threadedly coupled riser segments to assemble the riser 14.

The foregoing components, when fully assembled, comprising the riser 14, LMRP/BOP assembly 16, auxiliary lines 18, accumulator assembly 20 and fluid lines 22 form a well pressure control apparatus. In the present example embodiment, the one or more auxiliary lines 18 are separate from and are spaced at a selected lateral distance from the riser 14. The selected lateral distance may be related to a distance between the main drilling unit 10 and the auxiliary hoisting unit 12.

Referring to FIG. 2, a lower end 18A of the auxiliary lines 18 may be coupled to the accumulator assembly, as shown in and explained with reference to FIG. 3. As the auxiliary lines 18 are assembled through the floor of the auxiliary hoisting unit (12 in FIG. 1) the accumulator assembly is ultimately lowered to the water bottom (23 in FIG. 1). The auxiliary lines 18 may also have buoyancy devices (“cans”) 18B affixed externally thereto during assembly to provide buoyant force needed to prevent the auxiliary lines 18 from collapsing under their own weight in the water (24 in FIG. 1).

Referring to FIG. 3, the auxiliary lines (18 in FIG. 2) may be connected at their lower end (18A in FIG. 2) to the accumulator assembly 20 at a suitable connection therefor, e.g., as shown at 20A. Connection of pressure lines from the accumulator assembly 20 to the LMRP/BOP assembly (16 in FIG. 1) may be made through suitably pressure rated fluid lines 20B. The actual connection of the fluid lines 20B to the LMRP/BOP assembly (16 in FIG. 1) may be made after the riser (14 in FIG. 1) and the auxiliary lines (18 in FIG. 1) are fully assembled using a remotely operated vessel (ROV). In the present example embodiment, the auxiliary lines 18 may be assembled from pipe segments that provide the auxiliary lines 18 with internal pressure capacity of up to 20,000 psi (138,000 kPa).

FIG. 4 shows the LMRP/BOP assembly 16 in more detail. The LMRP part 17 may comprise a frame 17A on which may be mounted one or more accumulators 17B. The one or more accumulators 17B may have hydraulic fluid stored under pressure to selectively operate one or more rams 19A in the BOP part 19 of the LMRP/BOP assembly 16. A first connection 16A may be provided on the upper end of the LMRP/BOP assembly for connection of the LMRP/BOP assembly 16 to the lower end of the riser (14 in FIG. 1). A second connection 16B may be provided on the lower end of the LMRP/BOP assembly 16 for connection to the wellhead (22 in FIG. 1).

FIG. 5 shows an example of a portion of the riser 14, wherein one or more pipe segments 14A of the riser 14 have buoyancy devices (“cans”) 14A or similar devices disposed on the exterior thereof. Each pipe segment 14A may comprise a connector 14B at each longitudinal end, for example a bolt flange or a threaded connector. The connector 14B may couple each pipe segment 14A to an adjacent pipe segment 14A to assemble the riser 14.

When required, the riser 14 may be disassembled by reversing the above described assembly procedure using the main drilling unit (10 in FIG. 1) for the riser 14. The auxiliary lines 18 may be substantially contemporaneously disassembled using the auxiliary hoisting unit (12 in FIG. 1) to reverse the procedure explained with reference to FIGS. 1 and 2.

A riser assembly method according to the present disclosure may enable faster assembly and disassembly of the riser and auxiliary lines. The auxiliary lines may be capable of withstanding higher pressure than auxiliary lines known in the art.

Although only a few examples have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the examples. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. 

What is claimed is:
 1. A method for assembling a riser from a platform on the surface of a body of water, comprising: assembling segments of riser end to end through a drill floor using a main drilling unit on the platform; assembling at least one auxiliary line from segments connected end to end through an auxiliary hoisting unit on the platform, the auxiliary hoisting unit displaced laterally from a well center of the main drilling unit; and connecting the assembled riser to a wellhead proximate the bottom of the body of water.
 2. The method of claim 1 further comprising assembling a lower marine riser package and blowout preventer to a lower end of the riser at the beginning of assembling the segments of riser.
 3. The method of claim 1 further comprising connecting an accumulator assembly to a lower end of the at least one auxiliary line at the beginning of assembling the at least one auxiliary line.
 4. The method of claim 3 further comprising connecting the at least one fluid line from the accumulator assembly to a blowout preventer disposed at the bottom of the riser.
 5. The method of claim 1 wherein the at least one auxiliary line is assembled by threaded coupling of the segments thereof end to end.
 6. The method of claim 4 wherein the at least one auxiliary line comprises drill pipe.
 7. The method of claim 1 wherein the riser is assembled by coupling connectors at each longitudinal end of each segment of the riser to a corresponding connector at each longitudinal end of an adjacent segment of the riser.
 8. The method of claim 7 wherein the connectors comprise bolt flanges.
 9. The method of claim 1 wherein at least one of the riser segments has a buoyancy device coupled on an exterior thereof during assembly to the riser.
 10. A well pressure control system, comprising: a riser coupled at one end to an upper end of a lower marine riser package and blowout preventer assembly, a lower end of the lower marine riser package and blowout preventer assembly coupled to a wellhead disposed on top of a well, the riser extending to a platform on the surface of a body of water; at least one auxiliary line extending from proximate the bottom of the body of water to the platform, the at least one auxiliary line disposed at a selected lateral distance from the riser; and at least one fluid line hydraulically connected to a lower end of the at least one auxiliary line and connected to a part of the lower marine riser package and blowout preventer assembly.
 11. The system of claim 10 further comprising an accumulator assembly coupled to a lower end of the at least one auxiliary line.
 12. The system of claim 11 wherein the at least one fluid line comprises an hydraulic fluid line extending between the accumulator assembly and the lower marine riser package and blowout preventer assembly, the at least one fluid line selectively conducting hydraulic fluid under pressure to a blowout preventer part of the lower marine riser package and blowout preventer assembly.
 13. The system of claim 11 wherein the at least one fluid line comprises one of a choke line, a kill line and a boost line, wherein the at least one fluid line is in fluid communication with the well below the lower marine riser package and blowout preventer assembly.
 14. The system of claim 10 wherein the at least one auxiliary line comprises segments of pipe threadedly coupled end to end.
 15. The system of claim 10 further comprising at least one buoyancy device coupled to the at least one auxiliary line.
 16. The system of claim 10 wherein the riser comprises segments of pipe coupled end to end.
 17. The system of claim 15 wherein the segments of pipe are coupled end to end by a connector disposed at each longitudinal end of each pipe segment.
 18. The system of claim 17 wherein each connector comprises a bolt flange. 